Advantages and disadvantages of oral and intramuscular (IM) vitamin B12

Route	Advantages	Disadvantages
Oral	Outpatient visit not required Preferred for dietary deficiency Equal efficacy to intramuscular therapy	Adherence may not be assured Higher doses required for any condition that interferes with absorption For initial repletion of severe or symptomatic deficiency, there may be a concern about rapid and sufficient repletion; however, oral repletion can be effective for maintenance therapy if needed
Intramuscular	Adherence is assured (especially important for severe or symptomatic deficiency) Opportunity to interact with the medical team* Preferred for altered gastrointestinal anatomy or impaired absorption Less-frequent dosing after deficiency is corrected	May require outpatient visit (including nurse time, wait time, travel)^¶ Higher cost, which includes co-pay for visit and possibly a facility fee Extremely rare reports of hypersensitivity

Vitamin B12 to prevent or treat deficiency can be given orally (tablets, sublingual) or intramuscularly. The oral dose used to overcome impaired absorption is 1000 to 2000 mcg daily. The initial IM dose (can also be given as a deep subcutaneous injection) for adults is 1000 mcg daily, every other day, or weekly, depending on the severity of deficiency and clinical concern, followed by once monthly (cyanocobalamin) or once every two to three months (hydroxocobalamin). All patients should have an evaluation for the underlying cause.

Other routes are generally not used:

Intravenous – Not used due to concerns about excretion (mostly excreted in urine) and anaphylaxis, with rare exceptions such as in total parenteral nutrition.
Intranasal – Generally not used due to discomfort; oral route is likely to provide more consistent absorption.
Transdermal – Generally not used due to lack of data for efficacy.

IM: intramuscular.

* Some individuals have a strong placebo effect from the intramuscular injection and feel an immediate burst of energy; they may prefer to continue intramuscular injections.

¶ The requirement for outpatient visits and higher cost can be avoided by self-administration of B12 injections, which may be possible for some patients with appropriate training.

Graphic 142051 Version 3.0

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Advantages and disadvantages of oral and intramuscular (IM) vitamin B12